1 files changed, 118 insertions, 0 deletions
diff --git a/writeups/unaligned-mem/unamem.c b/writeups/unaligned-mem/unamem.c
new file mode 100644
index 0000000..cadfba1
--- /dev/null
+++ b/writeups/unaligned-mem/unamem.c
@@ -0,0 +1,118 @@
+#define _POSIX_C_SOURCE 200112L
+#include <stdio.h>
+#include <stdint.h>
+#include <limits.h>
+#include <error.h>
+#include <assert.h>
+
+#include <unistd.h>
+#include <wait.h>
+
+#define ARGV0 "unamem"
+#define DONT_FORK 1
+
+
+static void report_wait (const int status) {
+	if (WIFEXITED(status)) {
+		printf("exit %d\n", WEXITSTATUS(status));
+	}
+	else if (WIFSIGNALED(status)) {
+		printf("signal %d\n", WTERMSIG(status));
+	}
+	else {
+		printf("?\n");
+	}
+}
+
+int main (void) {
+	static char m[9]; // bss address is nicer than stack
+	char *c;
+	uintptr_t *p;
+	pid_t pid;
+	int status;
+
+	printf(
+		"CHAR_BIT:  %d\n"
+		"word:      %zd\n"
+		"uintptr_t: %zd\n"
+		"size_t:    %zd\n"
+		"short:     %zd\n"
+		"int:       %zd\n"
+		"long:      %zd\n"
+		"long long: %zd\n"
+		,
+		CHAR_BIT,
+		CHAR_BIT * sizeof(uintptr_t),
+		sizeof(uintptr_t),
+		sizeof(size_t),
+		sizeof(short),
+		sizeof(int),
+		sizeof(long),
+		sizeof(long long));
+
+	c = m;
+	p = (void*)(m + 1);
+
+	printf(
+		"malloc:    %zx", (uintptr_t)m);
+	for (size_t i = sizeof(uintptr_t); i > 1; i /= 2) {
+		if ((uintptr_t)m % i == 0) {
+			printf(" {%zu}", i);
+		}
+	}
+	printf("\n");
+
+	printf(
+		"c:         %zx\n"
+		"p:         %zx\n"
+		,
+		(uintptr_t)c,
+		(uintptr_t)p);
+
+	pid = DONT_FORK ? 0 : fork();
+	if (pid > 0) {
+		printf(
+		"access:    "
+		);
+		wait(&status);
+		report_wait(status);
+	}
+	else if (pid == 0) {
+		*p = UINTPTR_MAX;
+		*c = 0;
+		assert(*p == UINTPTR_MAX);
+		assert(*c == 0);
+
+		*c = 0;
+		*p = UINTPTR_MAX;
+		assert(*p == UINTPTR_MAX);
+		assert(*c == 0);
+	}
+	else {
+		perror(ARGV0": fork()");
+		return 1;
+	}
+
+	pid = DONT_FORK ? 0 : fork();
+	if (pid > 0) {
+		printf(
+		"float:     "
+		);
+		wait(&status);
+		report_wait(status);
+	}
+	else if (pid == 0) {
+		volatile float a, b, c;
+
+		a = 0.1;
+		b = 1.0;
+		c = b / a;
+		assert(c > 1.0);
+	}
+	else {
+		perror(ARGV0": fork()");
+		return 1;
+	}
+
+	return 0;
+}